This invention relates generally to movable bridges, and more particularly to double to leaf bridges, stabilizing devices for movable bridges, and center locks for movable bridges.
Movable bridges have been used for centuries to provide land vehicle or personnel passage across a body of water while allowing vessels to navigate on the waterway past the location of the bridge. The most common types of movable bridges include the swing bridge, which rotates about a vertical axis to remove its obstruction from the waterway, the vertical lift bridge which has a span over the waterway that can be lifted up sufficiently to clear a vessel navigating the waterway, and the bascule bridge that rotates about a horizontal axis at a right angle to the bridge or parallel to the waterway, swinging up and away from the navigation channel to clear it for vessels.
Movable bridges have generally been stabilized by the use of locking devices. A double leaf bridge has a pair of movable bridge sections, or leaves, which meet at or near the center of a navigation channel over which the bridge forms a removable roadway crossing, one leaf projecting from one side of the navigation channel, and the other leaf projecting from the other side of the channel. The typical bridge leaves open by rotating about axes which are at right angles to the bridge. The double leaf bridge usually has a mating pair of center lock devices rigidly attached to each of the bridge trusses or girders on each leaf. These devices, when the bridge is in the lowered position, engage to form a shear connection between the two leaves.
Prior art in this field has been limited in utility because of the tendency of the mating components of the center locks to wear due to contamination of the surfaces which slide while under live load and other forces.
Movable bridges consisting of roadway decks and minor structural members supported on bridge trusses or girders are required at many locations where highways or railways are required to cross navigable streams at a low elevation, where vessels navigating the stream cannot pass under the bridge but must have the bridge section over the navigable channel relocated temporarily to allow for the required vertical clearance. The double leaf bascule type of bridge is frequently used due to its economy of construction, ease and rapidity of operation, and minimal obstruction of the navigation channel. Most modem double leaf bascule bridges consist of two cantilever spans on opposite sides of a navigable waterway, arranged so that the spans rotate downward, driven by operating machinery, bringing their tips, or toe ends, to near proximity at the center of the channel to provide a passageway for vehicular traffic. A few double leaf swing bridges have been built which have features similar to double leaf bascule bridges, but which rotate about a vertical axis instead of a horizontal one to open the waterway for navigation and to reposition the bridge for carrying land highway traffic.
The weight, or dead load, of the extended leaves of the double leaf bridge and the traffic, or live load, upon the leaves is usually carried back to the piers in cantilever fashion. Center locks are deployed to link the tips of the two leaves together when closed, so that traffic load at the midportion of the span is shared by the leaves, and so that both leaf tips deflect approximately the same when the bridge is carrying traffic load and reacting to the effects of temperature changes, thus minimizing the discontinuity of the roadway surfaces at the meeting point of the two leaves, reducing or eliminating the bump experienced by a vehicle passing from one leaf to the other.
Typical center locks for a double leaf movable bridge are of one of three types: (1) a bolt that is thrust by mechanical means, from the end of each girder or truss on one leaf into a socket attached to the end of the corresponding truss or girder on the other leaf; (2) A pincer type mechanism, which may consist of male or female movable jaws, on one leaf which reaches out and grasps an extension on the other leaf; or (3) mating rigid male-female jaws mounted on the projecting ends of the bridge girders or trusses of each bridge leaf which interlock as the bridge is closed. The center lock components of these prior art devices suffer from impact and wear forces, resulting largely from deflection when under the influence of traffic loads.
The typical configuration of traditional center locks places high bearing pressure on components that move relative to each other when the bridge is carrying traffic and are exposed to contamination by road dirt, dust in the air, rain water and other contaminants. The result of the combination of high bearing pressure and contamination is rapid wear of the components, so that clearances increase, adding impact loads to the forces on the lock components, causing further increases in the rate of deterioration and allowing substantial misalignment of the two leaves at their meeting point. After a time, due to this deterioration, other bridge components, such as the span operating machinery and live load shoes, suffer more rapid degradation because of the worn-out condition of the center locks. Various schemes have rearranged the components of center locks, such as rotating them so that the lock bars are at right angles to the main bridge girders or trusses, without eliminating the problem of wear of components exposed to contamination.
This invention, by separating the components that move under live load conditions from the components that are exposed to contamination, provides movable bridges with center locks that are much more durable than those heretofore employed. This invention can be applied equally as well to double leaf bascule bridges of the simple trunnion type, rolling lift type, heel trunnion type, most other variations of double leaf bascule bridges, including those which incorporate multiple parallel sets of leaves, with multiple leaves on the same side of the navigation channel either connected or unconnected, and other types of movable bridges such as double swing bridges which have two separate leaves which meet over the navigation channel.
In a movable bridge supported on piers, having one or more pairs of opposing mating movable bridge leaf sections each of which includes a deck and main and minor support members and bearings upon which said movable bridge is mounted on said piers and live load bearings which contact said movable bridge when in position to carry traffic, the improvement invention includes a set of center locks engaging parallel to the axes of rotation of the movable bridge, driven by thrusting mechanisms at each mating pair of main bridge support members, thereby separately accommodating engagement and deflection of the bridge leaf sections.